1. Field of the Invention
This invention relates to tape machines for winding a tape, and more particularly, to a method and apparatus for accurately positioning a tape at a predetermined point by measuring in real time the inertia of the tape.
2. Description of the Prior Art
A magnetic tape is wound from a supply reel to a take-up reel on a tape machine. In performing tape operations with such a machine, it is often desirable quickly to position the tape at a predetermined point. For example, it may be desirable to position a magnetic tape containing audio information at the beginning of a musical selection which is located at a predetermined distance away from the beginning of the tape. In such an instance, the tape is advanced at a high speed in the so-called fast-forward mode of operation in order to position the tape at the predetermined point.
At least two methods have been used accurately to position a magnetic tape at a predetermined point. In one method, a fixed deceleration rate (or ramp) is applied to the tape when the tape is close to the predetermined point. In an alternate method, a variable deceleration rate or ramp is used to stop the winding of the tape. The variable deceleration rate or ramp is changed according to the amount of overshoot or undershoot which occurred in the last attempt to position the tape at the predetermined point.
The prior art methods of positioning a tape at a predetermined point suffer from significant drawbacks, however. The first method, using a fixed ramp, is very inefficient because the ramp must be calculated for the worst possible case which, of course, does not apply to all instances. When the tape is not the worst case, for example, it is not accurately positioned at the predetermined point. The second method, changing the ramp in accord with previous attempts, requires multiple attempts at positioning the tape at the predetermined point so that the amount of overshoot or undershoot can first be calculated and then applied to make the next attempt accurate.